1. Field of the Invention
The present invention relates generally to methods and apparatus for heating and maintaining temperature control of specimens under observation on a microscope stage. More particularly this invention relates to a device for maintaining very accurate temperature control around 37 degrees centigrade for purposes of biological research.
2. Description of the Prior Art
Prior methods for controlling the temperature of a specimen on a microscope stage have exhibited significant drawbacks. In one method an operator would merely sit with his microscope in a hot room which is controlled at the required temperature. The temperature of the specimens would then, presumably, be known to some accuracy and the operator would have full control over the microscope and all its accessories, such as manipulators and cameras. However, this system generally proved uncomfortable for the operator and accurate temperature control of the specimen was uncertain.
Another system proposed in the prior art required placing the microscope in a temperature controlled container from which the eye piece and the controls would protrude. Again, temperature control within the container proved uncertain and access to the specimen was difficult.
Consequently, efforts have been made in the industry to concentrate on a system providing specific local heat to the specimen. Efforts in this direction have been hampered by the limited dimensions available within which to provide the heater. Moreover, since the aperture in the microscope stage is quite large it interferes with the temperature control.
In one of such specimen heating systems, as shown in U.S. Pat. No. 3,472,726, there is provided a furnace having heating elements therein, a fan to pull cooling air past the specimen, an access opening for insertion of a microscope slide, and a heat deflecting lens through which the microscope will operate. But the elaborate nature and large size of this system has made it cumbersome and the temperature within the furnace difficult to control. Most importantly, however, it does not fit on a microscope.
In yet another device, described in U.S. Pat. No. 2,995,643, there is provided another version of the microscope oven. In this arrangement a chamber is described which is cooled by a water jacket to compensate for the thermal inertia of the system, and a heater is provided to circumscribe the specimen. An opening beneath the heating element is provided for insertion of a specimen slide. Again, the large size of this system yields limited versatility and it cannot be used with a traditional microscope stage.
More recently a device referred to as a Peltier unit has been developed and used for temperature control apparatus. These Peltier units are thermo-electric modules which either supply or remove heat depending on the polarity of the electrical connection. But, use of a Peltier unit on a microscope stage is difficult due to its size and opacity; and its temperature control is difficult due to the temperature overshoot and thermal lag involved in its control. This difficulty was dealt with in a recent improvement for temperature control apparatus. Although not used on microscope stages, U.S. Pat. No. 4,066,365 describes an electrical circuit having a cascade of Peltier units and a plurality of temperature sensors employed to minimize temperature overshoot and thermal lag.
The mainstay of the industry has been and currently is a water reservoir system such as that described in U.S. Pat. No. 2,228,906. In that device, a water container having a pump system and a heater device therewith is used to deliver water of a regulated temperature to a jacket in a microscope stage. In such a system, the temperature control of the microscope stage and the specimen are difficult due to heat loss between the reservoir and the stage. Further, since the heating function is performed in the water reservoir the thermal lag and overshoot create a significant problem.
As an alternative to the water reservoir, some attempts have been made to heat the microscope stage through other means. For one example, the stage has been heated with infra red radiation with little success. In yet another example, electrical heating coils have been used to generate the heat. One system uses a conducting plate to convey the heat to the microscope stage, while another wraps the coil around the stage. But both of these coil systems generate too much electrical inductance and thermal inertia for accurate temperature control. Absent a complicated controller such as that described in U.S. Pat. No. 4,066,365, these coil systems tend to overshoot the desired temperature and are of limited use.
Accordingly, it is a principle object of the present invention to provide an improved microscope stage which has low thermal inertia and which may be accurately brought up to a desired temperature with minimal overshoot.
It is a further object of the present invention to provide means for heating a microscope stage and providing temperature control in and about the aperture in the microscope stage attachment and to provide means for accurately heating and maintaining the temperature in a specimen dish.
It is yet another object of the present invention to provide thermal isolation means to thermally separate the heating stage attachment from the microscope stage.
Finally, it is an object of the present invention to provide a non-inductive thermal heating stage to eliminate magnetic fields and inductive effects.